The levels of evidence [A-D] supporting the recommendations are defined at the end of the "Major Recommendations" field.
Detection and Follow-up of Adenomas
- Screening is justified on the basis of the assumption that removing adenomatous polyps from symptomless individuals reduces the incidence of and mortality from colorectal cancer
- The prevalence of adenomas in unselected autopsy series is as high as 30%.
Symptomatic Patients
- If a polyp is detected, the whole colon should be examined and all polyps removed.
- If colonography suggests a polyp not exceeding 5 mm in diameter in a patient above 75 years of age, there is no absolute indication for colonoscopy and polyp removal.
- Suspicion of a polyp in a young patient or a polyp exceeding 5 mm in diameter is always an indication for colonoscopy.
Asymptomatic Persons
- The use of colonoscopy for screening of asymptomatic individuals is indicated only in cases with marked familial susceptibility to cancer or if an adenoma has earlier been removed endoscopically.
- Follow-up after the initial investigations is not indicated in persons with a single small tubular adenoma in the rectum or in patients above 75 years of age.
- Individuals with a history of one large adenoma or several adenomas of any type should undergo screening colonoscopy at 3 to 5-year intervals.
Preventive Measures
Although diet is considered to be a major environmental cause of colorectal cancer, there is insufficient evidence to recommend dietary changes for prevention. On the other hand, the diet suggested for prevention, with a reduced content of fat and energy along with an increased content of fruit and vegetable fibre, is in accordance with recommendations for the treatment and prevention of other diseases.
Population-based Screening
The results of large trials involving screening for faecal occult blood indicate a reduction in mortality from colorectal cancer (Towler et al., 1998) [A], but such screening results in colonoscopy being performed on a large proportion of the screened population. The cost-effectiveness of screening is controversial. Only about 50% of those invited can be expected to attend screening (Vernon, 1997; The Database of Abstracts of Reviews of Effectiveness (DARE)-971223, 1999) [B].
Screening Family Members of Cancer Patients
Always obtain a thorough family history from a patient with colorectal cancer. If there are cases of colorectal cancer or other adenocarcinomas (e.g., of the breast, uterus, or ovaries) in the family, consider the possibility of familial cancer and screening of the relatives (Brewer et al., 1994; DARE-954069, 2001) [C].
Examining a Symptomatic Patient
Patients with colorectal cancer often present with non-specific gastrointestinal problems. Because both the sensitivity and specificity of faecal occult blood are rather poor, a negative result does not exclude colorectal cancer in a symptomatic patient.
Related Evidence
- The presence of neoplasms in the distal colon increases the risk of advanced neoplasia in the proximal colon; however, about 50% of patients with proximal advanced neoplasms have no distal polyps (Lieberman et al., 2000; Imperiale et al., 2000) [A].
- The potential benefits of dietary fibre in the prevention of colorectal adenomas and carcinomas are not evident in randomized controlled trials with 2 to 4 year follow up (Asano & McLeod, 2002) [C].
- High dietary garlic consumption seems to be associated with decreased risks of laryngeal, gastric, colorectal, and endometrial cancers and adenomatous colorectal polyps, but evidence from controlled studies is lacking (Agency for Healthcare Research & Quality [AHRQ], 2000; Health Technology Assessment Database: HTA-20010948, 2004) [D].
- Daily intake of 1 gram dietary calcium may have moderate protective effect on development of colorectal adenomatous polyps, but the evidence is insufficient to recommend general use of calcium supplements to prevent colorectal cancer (Weingarten, Zalmanovici, & Yaphe, 2003) [C].
- Antioxidant supplements cannot be recommended for gastrointestinal cancer prevention. The potential cancer preventive effect of selenium should be studied further (Bjelakovic et al., 2004) [A].
Definitions:
Levels of Evidence
- Strong research-based evidence. Multiple relevant, high-quality scientific studies with homogenic results.
- Moderate research-based evidence. At least one relevant, high-quality study or multiple adequate studies.
- Limited research-based evidence. At least one adequate scientific study.
- No research-based evidence. Expert panel evaluation of other information.
